PCBs Hit IVF Pregnancy Success

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An environmental pollutant present in most humans can
significantly lower the chances of a woman conceiving via in
vitro fertilization, according to new research, a finding that
also may extend to women trying to conceive naturally.

While the new work directly addresses the growing segment of the
population conceiving via IVF, it's likely to also have
implications for women trying to conceive the old-fashioned way,
because PCBs may affect all conception similarly. Other studies
are consistent with this possibility.

So-called PCBs are chlorinated organic chemicals that were once
widely used in industry and consumer goods, often as insulating
and cooling fluid in electrical transformers and capacitors.
Found to have numerous health effects, they were banned in the
late 1970s. PCBs have been linked to, among other things, higher
cancer rates and developmental abnormalities in infants. Also,
PCBs are highly resistant to degradation, so they persist in our
environment.

"PCBs have been associated with a number of effects in
experimental animals and human studies, many of those associated
with reproduction," said study leader John Meeker of the
University of Michigan School of Public health. Other studies,
for example, have indicated that women with higher levels of PCBs
take longer to become pregnant than women with lower levels.

The new work, published today in the journal Environmental
Health Perspectives, found that the women in the top quarter
of blood PCB levels had twice the odds of a failed embryo
implantation as those in the quartile with lowest blood PCBs.
They also had 41 percent lower odds of the in vitro ultimately
resulting in the birth of a child.

A doubling of the odds of implantation failure, "is large,"
Meeker said. "It does suggest that while there are probably many
factors involved in implantation, this particular exposure might
be one of them."

However, the women in the study weren't from a population with
extreme levels of PCBs, such as would be seen in Inuits, or
Swedish fishermen's sisters or Taiwanese women suffering from
contaminated cooking oil exposure. So, even more or less within
the distribution of levels in the normal population, this effect
appears.

The researchers do not know whether the slightly elevated median
levels could have something to do with the women's infertility,
or whether they just reflect differences in the timing of the
measurements, because PCB levels in the population are declining
and their measurements predate those representing the general
population.

Today, most human exposure comes from contaminated food,
primarily fish, but also meat and dairy sources. Like other
persistent organic pollutants, they concentrate in fat in
long-lived animals higher up the food chain, making certain fish
particularly high in PCBs. Removing skin and fat from fish
reduces their PCB content.

The new study, by looking at a population where conception is
being monitored closely, could put a finer point on what stage of
conception and pregnancy might be most sensitive to PCBs.

"It gives us an opportunity to study endpoints that aren't
normally observable in humans," Meeker said. "In the normal
population, this goes as an undetected pregnancy and could
contribute to increased time to pregnancy."

"This is a very interesting paper and one that suggests select
environmental chemicals may be associated with adverse
reproductive outcomes including early pregnancy loss," said
Germaine Buck Louis of the National Institute of Child Health and
Human Development in Bethesda, Md.

"This unique study population provides important insight into the
relation between hormonally active environmental chemicals such
as PCBs and a spectrum of reproductive outcomes during some of
the most sensitive windows of human development," she said.